Help with smoothed MA's

[bozza]

I have done the formula for a smoothed ma on a spreadsheet to try and back test a theory but the smoothed ma on the spreadsheet doesn't match the smoothed MA on the metatrader chart. On a half hour chart GBPUSD the chart says the 7 period smoothed ma is 1.6267 where if you work it out as per formula on a spread sheet it works out to b 1.6255 which is a big difference. I can't seem to work out why this is, can anyone shed any light, it would be much appreciated.

Regards Bozza